Dyson spheres — technology wrapped around an entire star to maximize energy use — would be unimaginably big. But the idea of maximizing the light from a central star certainly makes sense. Imagine a sphere with a radius at the distance of Earth’s orbit. Now you’ve got a surface area more than 100 million times what’s available on our planet, a sensational venue for science fiction if nothing else. And you’re certainly changing the energy equation — our total power consumption today is the equivalent of about 0.01 percent of the sunlight falling on Earth, according to a new article in New Scientist. Keep energy demand growing at 1 percent per year and in a single millennium we’ll need more energy than strikes the surface of the planet.
Moving power generation into space is certainly something that would motivate a civilization a good deal more advanced than our own, and using abundant asteroid material, it could spread power generation entirely around the star. Stephen Battersby, who wrote Alien Megaprojects: The Hunt Has Begun, doubts they would create a single shell because it would be gravitationally unstable. But a Dyson ‘swarm’ is more plausible, with hordes of large power stations moving on independent orbits around the star. Dyson, who likes to talk about what is observable rather than what’s probable, thinks we could spot such a project through its waste heat in the infrared.
This wouldn’t be an easy catch because there are astronomical configurations — a young star in an envelope of gas and dust, for example — that radiate in the infrared in much the same way. But this, says Battersby, can be resolved:
…the infrared spectrum of these objects should be a giveaway. Silicate minerals in dust produce a distinctive broad peak in the spectrum, and molecules in a warm gas would produce bright or dark spectral lines at specific wavelengths. By contrast, waste heat from a sphere should have a smooth, featureless thermal spectrum. “We would be hoping that the spectrum looks boring,” says Matt Povich at the California State Polytechnic University in Pomona. “The more boring the better.”
Image: A mosaic of the images covering the entire sky as observed by the Wide-field Infrared Survey Explorer (WISE), part of its All-Sky Data Release. Since the Infrared Astronomical Satellite mission of 1983, we have added greatly to our databases of infrared objects. Will new searches help us locate a source with a clearly artificial signature? Image credit: NASA/JPL-Caltech/UCLA.
And that brings us to Vyacheslav Ivanovich Slysh, a Russian radio astronomer known for the so-called ‘Slysh formula,’ which helps determine the size of sources of synchrotron radiation, an important contribution to the study of active galactic nuclei. Known as well for his work on maser emission in star-forming regions, Slysh turned his attention in 1985 to a survey of infrared data in the hunt for Dyson objects, whether spheres or swarms. Battersby mentions Slysh only in passing, but the Russian work on what I usually refer to as ‘interstellar archaeology’ in these pages is quite interesting. In 2000, Slysh’s work was followed by M. Y. Timofeev, collaborating with Nikolai Kardashev, both efforts using data from the Infrared Astronomical Satellite.
Centauri Dreams readers will know to associate the search for extraterrestrial artifacts with Richard Carrigan, a scientist emeritus in the Accelerator Division at the Fermi National Accelerator Laboratory whose most recent search dates from 2009. Here’s what Carrigan says about the Slysh and Timofeev efforts in his Dyson Sphere Search History. Here he has just referred to a search by Jun Jugaku and Shiro Nishimura, looking for ‘partial’ Dyson spheres:
Slysh and Timofeev at al. have used the IRAS database for a different approach. Slysh investigates the flux at the maximum of a Dyson Sphere spectrum. He estimates that all Dyson Spheres with temperatures from 50 to 400 ºK within 1 kpc of the sun should have been detected. The Timofeev search looked at a population of IRAS sources in the 110-120 and 280-290 ºK temperature range as established by Kardashev and others and did Planck blackbody fits to the four IRAS bands. They fitted by minimizing to a Planck distribution. (Note that no Planck spectrum correction is made on the four measured fluxes from the filters.) Slysh identified one possible Dyson Sphere candidate, G357.3-1.3. The Timofeev at al. search identified 10 or so candidates but ruled out most of them, often on the basis of associations.
That figure of 1 kiloparsec (kpc) from the Sun identified with Slysh is chosen for a reason. In 1966, Carl Sagan and Russell Walker published a paper in The Astrophysical Journal on “The Infrared Detectability of Dyson Civilizations.” Their analysis showed that a search out to 1000 parsecs should be possible even with the technology of the day, but noted the problem of confusing a possible Dyson signature with natural phenomena. Carrigan’s 2009 search also used the IRAS data of 250,000 infrared sources (it covers 96 percent of the sky), looking for both full and partial Dyson spheres in the blackbody temperature region from 100 K to 600 K. Carrigan’s limits don’t go out as far. He says that IRAS’ Low Resolution Spectrometer was sensitive enough to find Dyson spheres out to 300 parsecs. That would encompass roughly a million solar-type stars.
Image: Richard Carrigan, who told New Scientist for its recent article: “I wanted to get into the mode of the British Museum, to go and look for artifacts.”
I’ve mentioned enough papers to begin a small bibliography, which I’ll list here, but go to Carrigan’s site for other references. I bring all this up for two reasons. First, new searches for extraterrestrial artifacts are in the works, about which more tomorrow. The other reason is that this work isn’t highly visible, but the change it represents from more conventional radio and optical SETI methods is profound. The change speaks not so much to the failure of earlier SETI to produce a result as to our growing understanding that civilizations substantially more advanced than our own — if they exist — could work with engineering on mind-boggling scales. Such engineering should be detectable, and we’ll look at new efforts to find it tomorrow.
The Slysh paper is “A Search in the Infrared to Microwave for Astroengineering Activity,” in The Search for Extraterrestrial Life: Recent Developments, M. D. Papagiannis (Editor), Reidel Pub. Co., Boston, Massachusetts, 1985, p. 315. Timofeev and Kardashev wrote “A Search of the IRAS Database for Evidence of Dyson Spheres,” Acta Astronautica 46 (2000), p. 655. The Sagan and Walker paper is “The Infrared Delectability of Dyson Civilizations,” Astrophysical Journal 144 (3), (1966), p. 1216. And Richard Carrigan’s 2009 study is “The IRAS-based Whole-Sky Upper Limit on Dyson Spheres,” Astrophysical Journal 698 (2009), pp. 2075-2086, available online.